Process of quick tannage by means of the one-bath method



Patented June 1, 1926.

-UNITED STATES 135 x019- VPATI'EYNT FRANZ MERKEL, OF OFFENBACfi-ON-THE-MAIN,

FABRJI GRIESHEIM-ELEKTRON,'OE FRANKFORT-ON-THE-MAIN, GERMANY A C03 PORATION.

GERMANY, nssrezuon TO cam-ism rnocnss or eurcx TANNAGE IBY'MEANS or THE ONE-BATH mn'rnonno Drawing. Application filed m 1s, 1922, Serial No. 575,763, and in Germany August 1, 19:21.

Processes have already-been proposed in which hide is tanned into leather by treatment with a solution of a salt of the metal chromium, for example, chromium chloride,

5 which may be the normal salt or a basic chloride, see for example, U. S. patents to Dennis Nos. 495,028 and 511,411, which shows such a process.

I have nowfound that than has heretofore been obtained by the use of a trivalent chromium salt by means of the one-bath process,this quick result depending upon the use of the metal salt, in a highly concentrated condition. The unexpected result is produced,

a quicker tannage due to the high concentration of the salt, that the possibility of electrolytic dissociation in the salt of the tanning liquor during the process of tanning is prevented, and by keep- 0 ing up the quantity of chromium salt in the bath necessary for complete tanning of the' hide, the amount of liquor being less than one-third of the weight of the unhaired skin.

There being substantially no electrolytic. dissociation of the chromium salt used, there is not produced in the liquor at any time, any

high concentration of free acid, and'on account of the shortness of time of the tanning process, the hide is not in any way injured by the presence of the free acid in the liquor.

In the usual one-bath method heretofore employed, where basic sulfates of chromium were used, a solution of about 8 B., was employed, the quantity of liquor being approximately the weight of the unhaired skins, for example, sheep skins. In such a process, sheep skins are found to be tanned through in about four to six hours, whereas skins of beef cattle, require one to'two days.

On the contrary in accordance with the present invention, by using solutions of chromium salts of about to B.. and a siderably reduced quantity of liquor, it is possible to thoroughly tan furs, sheepskins, box calf, and similar thin skins, in about ten to twenty minutes, and heavier skins such as those of cattle requiring only one to three hours.

50 The tanning liquor is preferably composed of basic chlorides, such as basic chromium chloride, and especially those basic chlorides which possess an easy solubility in water, as these are subject only slightly to hydrolproduced, can be.

v of illustrating the same, and in these exam- 75 ysis or electrolytic dissociation, and {furthermore these salts are relatively cheap.

' Also basic sulfates or mixtures of basic chloridesand basic sulfates, 0r other-basic salts; of chromium can be similarly used. Contrary to the previous practice, it is advisable to begin immediately with the whole quantity of chromium compound in the liquor, instead "of the usual method which involves gradual additionof the tanning agent to the liquor or immersing first in dilut'eliquors, then in somewhat more concentrated liquors. It has. been found that there is no production of wrinkles in the grain which might be looked for when using a highly concentrated tanning solution on the raw hides.

Without restricting myv invention, the following examples are given for the purpose ples, parts are by weight.

Example 1.

parts of well cleaned and neutral (free from l I Into an empty tanningdrum is placed 100 through the hollow axle of the rotating [1 drum, .is added oxid, based upon the quantity of salt used,

- and hence corresponding to about-one-half can be run in rapidly.

basic. The liquid The drum is rotated in the liquor, the skins are whether the it is noticed for tumbling the skins for ten to twenty minutes, and then tested by-cuttlng, to show whether the liquor has assumed a pale green color showing the skins to have taken up substantially all of the chromium compound. About 10 parts of fine common salt (or other neutral salt, such as sodium about 10 parts of a solution of chromium chloride .of 50 B., such solu tion also containing about 25% of chromium I hide is tanned through, and also ed in the lime pit ten minutes in the drum with running water, then smoothed down, shaved and then the final neutralization is eifected with about 3 to 4 per cent of borax or sodium bicarbonate. With this final neutralization, the coloring of the skins can begin. For making black kid, the skins are colored with chrome leather black, treated with shumac extract, and may be oiled with sulphonated oils. By the process of this example, a close grain black colored leather suitable for shoe uppers is produced which is very strong.

Example 2.

100 parts of cattle skin having been treatfor removal of the hair, and then well rinsed are, first pickled in a rotating tumbling drum with 6 to 10 parts of salt, and 1.5 to 2.5 parts of hydrochloric acid of 20 B., and 100 parts of cold water, say 20 C. The skins may advantageously be allowed to stand in the pickle over night. 10 to 14 parts of liquid chromium chloride containing 25% of oxid, (Cr O and without any addition of water are added and run into the drum. The drum is rotated from one to three hours according to the thickness of the skin, whereon the tannage may be considered as finished. This is easily recognized by'an equal green color over the whole of a cut surface of the leather. The solution or liquor in the drum will be found to be almost free from chromium, whichis shown by absence'of strong green color. Then 6 to 10 parts of common salt in dry form are added (or a like amount of other neutral salt) and the hides are drummed again for about an hour. They are then rinsed in the drum with running water for ten to fifteen minutes after which the neutralization is efl'ectedby sodium bicarbonate. After being well rinsed again by running water in the drum, an absolutely neutral leather is produced. This can then be subjected to coloring or lubricating, or can be left lying in the water over night and the coloring and lubricating effected the next day. The oiling can be done by hand with fish oil or moelle'n degras. The leather is then finished in the usual way, dried, stretched, if desired, in the half dry condition. The toughness and contracting strength of leather belting produced in this manner are extremely good.

The stretching coeflicient, when the leather belt becomes wet is very little. In this example instead of 10 parts of chromium chloride, 15.6 parts of chrome alum, can be used, sodium bicarbonate being used for the neutralization step.

I claim:

1. A process of quick tannage with a solution of a trivalent chromium salt, by the onebath process, which comprises applying the metal salt directly tothe hide in the form of a highly concentrated solution, and thereby reducing to a minimum any injury to the hide by protracted contact of the leather undergoing treatment with the products of electrolytic dissociation in the tanning liquor during the tanning process.

2. A process of rapid tanning in which hide is treated with not substantially more than a third of its weight of a concentrated solution of a basic salt of chromium, such solution containing a sufiicient amount of such chromium compound for-the complete tanning of the hide.

3. A process of rapid tanning in which hide is treated with not substantially more than a third of its weight of aconcentrated solution of a basic chromium chlorid, such solution containing asuflicient amount of basic chromium chlorid for the complete tanning of the hide.

4. A process of rapid tannin which comprises treatmg hides or skins with a tanning solution containing a high concentration of a trivalent chromium salt, such concentration being not substantially less than that corresponding to 25 B.

5. A process of rapid tannin which comprises treating hides or skins wlth a tanning solution containing a high concentration of basic trivalent chromium salt, such concentration being not substantially less than that corresponding to 25 B.

6. A process of rapid tanning which comprises treating hides or skins with a tanning solution containing a high concentration of basic chromic chloride, such concentration being not substantially less than that corresponding to 25 B.

7. A process of rapid tanning which comprises subjecting hides or skins to the action of a basic chromic salt in sufficient quantity when in a liquor to be not substantially less than 25 B., the amount of such liquor be ing less than about one third of the weight of the hides or skins.

Signed at Frankfort a/m., in the Province of Hesse-Nassau and State of Germany, this 27th day of June A. 1)., 1922.

FRANZ MERKEL. 

